Permian period Jurassic period Pennsylvanian period Mississippian period 44m学206my251my300m￥20m 354my period Silurian eriod Evolution of 543 my. cells with 35 m.y Cambrian 2b.y Tertiary period Oldest fossil cells 4.6 billion 46y years ago ERA Pleistocene PERIOD Oldest rocks epoch EPOCH dated on Earth Holocene epoch 生物的演化生物的演化